Not applicable.
1. Field of the Invention
The invention relates to a reactor for performing a catalytic reaction, associated with a thermal effect, of substances contained in a gas flow comprising
a) a housing having an inlet and an outlet for the gas flow;
b) at least one bed of catalyst material which at least partially fills the interior of the housing;
c) at least one temperature regulating device which is surrounded, at least in parts, by the bed of catalyst material and can be traversed by a heat carrier medium.
2. Discussion of Relevant Art
Reactors of this type are described in DE PS 37 08 957, EP PS 0 260 530 and EP PS 0 431 078. All these publications describe the use of such reactors in the form of the example of recovering sulphur from a gas containing hydrogen sulphide and additionally carrying, or mixed with, oxygen. The catalytic, and in this case exothermal, reaction yields elementary sulphur and water. The corresponding reaction equations are given in EP PS 0 431 078.
The reactor according to the invention is also particularly intended for the recovery of elementary sulphur from gases containing hydrogen sulphide, but is not limited to this application. It can be used in all cases in which substances entrained by the gas flow are to be converted into a desired end product in a catalytic reaction which is associated with a thermal effect and thus takes place exothermally or endothermally. The reactor facilitates optimal spatial temperature profiles, as are required to achieve the highest possible local reaction speeds and/or for setting the desired reaction equilibrium value.
Since, as mentioned, heat is consumed (endothermally) or released (exothermally) in the chemical reactions of interest here, using a temperature regulating device it is necessary to supply or discharge reaction heat and to maintain the temperature of the catalyst bed within a specific range (e.g. temperature window). In the case of exothermal catalytic reactions, the overshooting of a maximum temperature value could, for example, have different disadvantageous results: On the one hand, the materials from which the reactor is composed, as well as the catalyst material, could of course suffer damage. Furthermore, other substances entrained with the gas flow could decompose in an undesirable manner. In general, in addition to the desired reactions (be these endothermal or exothermal), undesired competing reactions could also occur and/or, upon departure from a specific temperature window, the reaction equilibrium could shift undesirably in a specific direction.
In the case of the known reactors of the type referred to in the introduction and described in detail in the above mentioned publications, on account of the exothermal process the temperature regulating device consists of a cooling device in the form of a wound tubular coil. However, such cooling devices are extremely costly to produce, difficult to service and virtually impossible to remove from the reactor housing. As, furthermore, the path of the coolant through coils wound in this way is very long, a substantial change occurs in the temperature of the coolant on its path through the cooling coil, and the development of the desired temperature profile within the catalyst bed either is not very precise or necessitates additional cost-increasing measures.
The object of the present invention is to develop a reactor of the type referred to in the introduction such that it can be produced cost-effectively and is easy to service.
This object is achieved, in accordance with the invention, in that
d) the temperature regulating device is formed by a plurality of pairs of straight tubes which are connected to one another via a U-shaped section (xe2x80x9cU-tubesxe2x80x9d) and the straight sides of which extend in parallel, one side of each U-tube leading into a first distribution chamber which can be supplied with heat carrier medium and the other side of each U-tube in each case leading into a second distribution chamber from which the heat carrier medium can be discharged.
In accordance with the invention, the temperature regulating device thus no longer consists of a coil, which is difficult to produce, but of U-tubes. Here xe2x80x9cU-tubexe2x80x9d is to be understood as a structure whose sides consist of two straight tubes connected to one another at one end via a U-shaped section. The production of such U-tubes is extremely simple. Each of these U-tubes is separately traversed by heat carrier medium so that the path along which heat is absorbed or emitted is relatively short and the change in temperature of the heat carrier medium upon its traversal of each individual U-tube is relatively small. The connection of the individual U-tubes to the heat carrier medium cycle is very simple due to the distribution chambers provided in accordance with the invention. If necessary, individual U-tubes of the overall arrangement can be removed, repaired or replaced, thus considerably simplifying the servicing of the reactor according to the invention. By changing the distribution of the tubes, the tube bundle can be adapted to different heat transfers within the catalyst bed without the incurrence of additional costs.
Preferably the sides of each U-tube span a plane extending in parallel to the direction of flow of the gas through the reactor. The two sides of each U-tube, which naturally are at different temperatures, thus occupy positions of the flow path which can and should be at different temperatures. In this way, within the catalyst bed it is possible to obtain isothermal surfaces which are substantially flat and extend at right angles to the direction of flow of the gas through the reactor.
Expediently the U-tubes are distributed between a plurality of planes in each case spaced from one another. In this way the sides of the U-tubes fill the corresponding region within the catalyst bed. The cooling surface density which is obtained can be spatially constant or if necessary can also be a function of the location.
A particularly preferred embodiment is that in which a plurality of U-tubes are arranged in a plane such that an outermost U-tube is provided whose semi-circular bent section has a maximum radius, and in which at least one further U-tube is arranged between the sides and the semi-circular bent section of said outermost U-tube, the semi-circular bent section of said further U-tube having a somewhat smaller radius such that the further U-tube extends in parallel to the outer U-tube in the same plane. In this arrangement the U-tubes arranged in the same plane can, as it were, be internested, which considerably simplifies the connection of the two sides forming part of the various U-tubes to the corresponding distribution chambers. In this way the U-tubes within the same plane need not intersect.
Preferably, the distribution chambers are formed in a head piece which can be detachably secured to a main part of the housing. The removal of this head piece renders the interior of the reactor housing accessible; at the same time the distribution chambers of the assigned assemblies can easily be serviced when required.
In this case it is particularly favourable if the U-tubes are (also) attached to the head piece. With the head piece removed, the U-tubes can then be extracted together with the head piece from the main part of the reactor housing and if necessary serviced.
If the reactor is relatively large, it is advisable to attach a support frame to the head piece, said support frame itself bearing, at a distance from the head piece, at least one grid through which the sides of the U-tubes extend such that they are supported by the grid. In this way the U-tubes no longer are only directly attached to the head piece in freely projecting manner but are relieved of load by the grid or grids so that the fixing points of the U-tubes are not subjected to impermissibly large bending moments.
A metallic web, itself bearing the bed of catalyst material, can be arranged above the support frame. In this way, upon the removal of the U-tubes, the bed of catalyst material can also be removed from the housing and if necessary replaced.
The brunt of the temperature control can be undertaken by the temperature regulating device formed by a plurality of U-tubes. If an extremely accurate and fast responding adjustment of the temperature control is additionally desired, it is possible to employ an embodiment of the invention wherein a plurality of gas lances are arranged in the vicinity of the sides of the U-tubes adjacent to the gas inlet, said gas lances being able to be supplied with gas as additional heat carrier medium orxe2x80x94in the case of stepped reactionsxe2x80x94with additional reagents. If, for example in the case of an exothermal reaction, it is necessary for the catalyst bed to be additionally rapidly cooled on the side adjacent to the gas inlet (where experience has shown the maximum temperatures to occur), inert gas not participating in the reaction can be supplied with an appropriate temperature and quantity via the gas lances. This cooling can be very finely dosed and is fast acting.
It is expedient if all the gas lances (also) lead at one end into a third distribution chamber which is formed in the head piece.
In all of the above described cases it proves particularly favourable for the sides of the U-tubes to extend horizontally. With this construction the longer dimension of the reactor housing is aligned horizontally; via the removable head piece the interior of the housing is then accessible from one side. U-tubes and optionally catalyst bed can be moved or pushed out of the reactor housing in the lateral direction. No lifting movement of these heavy parts is required; it is unnecessary to provide a particularly large headroom to obtain access to the inner parts of the reactor.
If necessary, a plurality of temperature regulating devices of the described type can also be arranged in series in a reactor, it also being entirely possible to employ different heat carrier media in the individual temperature regulating devices.